It’s clear that the density of cities makes human beings as a species more productive. But cities can also have deleterious effects on our cognition, according to this most interesting report from the Boston Globe (via Planetizen). In a series of studies, psychologists and urbanists are finding that the city-life assaults our brains with all sorts of stimuli overloading our cognitive capacity.

For the first time in history, the majority of people reside in cities. For a species that evolved to live in small, primate tribes on the African savannah, such a migration marks a dramatic shift. Instead of inhabiting wide-open spaces, we’re crowded into concrete jungles, surrounded by taxis, traffic, and millions of strangers. In recent years, it’s become clear that such unnatural surroundings have important implications for our mental and physical health, and can powerfully alter how we think …

Consider everything your brain has to keep track of as you walk down a busy thoroughfare …  There are the crowded sidewalks full of distracted pedestrians who have to be avoided; the hazardous crosswalks that require the brain to monitor the flow of traffic … There’s the confusing urban grid, which forces people to think continually about where they’re going and how to get there.

The reason such seemingly trivial mental tasks leave us depleted is that they exploit one of the crucial weak spots of the brain. A city is so overstuffed with stimuli that we need to constantly redirect our attention so that we aren’t distracted by irrelevant things, like a flashing neon sign or the cellphone conversation of a nearby passenger on the bus. This sort of controlled perception — we are telling the mind what to pay attention to — takes energy and effort. The mind is like a powerful supercomputer, but the act of paying attention consumes much of its processing power.

Natural settings, in contrast, don’t require the same amount of cognitive effort. This idea is known as attention restoration theory, or ART, and it was first developed by Stephen Kaplan, a psychologist at the University of Michigan. While it’s long been known that human attention is a scarce resource — focusing in the morning makes it harder to focus in the afternoon — Kaplan hypothesized that immersion in nature might have a restorative effect.

Imagine a walk around Walden Pond, in Concord. The woods surrounding the pond are filled with pitch pine and hickory trees. Chickadees and red-tailed hawks nest in the branches; squirrels and rabbits skirmish in the berry bushes. Natural settings are full of objects that automatically capture our attention, yet without triggering a negative emotional response — unlike, say, a backfiring car. The mental machinery that directs attention can relax deeply, replenishing itself.

So this explains why I not only recharge at the beach, but focus and think better there – because life is easier and more natural. Seriously, this research has implications for urban design and for work and career management as well. Location continues to matter in more and varied ways than we think.